There are numerous occasions when it is necessary to determine the flatness of an article. For example, magnetic steel laminations produced by a stamping operation must be held within a specified degree of flatness so that a lamination stack of specified width contains the proper volume of material. By checking random samples of lamination stampings, one can take corrective action to keep flatness within the specified limits by adjusting the stamping machine and/or using different material for the stampings.
Norberg U.S Pat. No. 4,560,924 discloses a flatness measuring apparatus including oppositely disposed capacitive probes which move across a flat reference surface and an object surface, respectively, as a carriage is moved in lateral increments. A first capacitor is formed by one of the probes and the object surface, while a second capacitor is formed by the remaining probe and the reference surface. The capacitances of the two capacitors are translated into distance values which are utilized to generate numerical information describing the flatness of the object surface.